Recently, from the viewpoint of energy saving or environmental conservation, illuminating apparatuses (such as LED lamps) using a light-emitting diode (hereinafter, also referred to as “LED”) as a light source have been used instead of incandescent lamps. However, a conventional illuminating apparatus using an LED as a light source can emit light only in the forward direction, but cannot emit light in all directions like an incandescent lamp. Accordingly, the conventional illuminating apparatus cannot extensively illuminate a room using reflected light from a ceiling or walls like an incandescent lamp.
In order to make light distribution characteristics of such a conventional illuminating apparatus using an LED as a light source close to the light distribution characteristics of an incandescent lamp, it has been proposed that the distribution of light emitted from the LED be controlled by the use of a light flux controlling member (for example, see PTL 1). FIG. 1 is a schematic diagram illustrating the configuration of an illuminating apparatus described in PTL 1. As shown in FIG. 1, illuminating apparatus 10 includes plural LEDs 12 arranged on a substrate and cylindrical case 14 formed of a light-transmitting material and disposed around LEDs 12. The top surface of case 14 is formed in an inverted truncated cone shape. Aluminum plate 16 reflecting light is attached to the oblique surface of the truncated cone, which serves as a reflection surface. On the other hand, the horizontal plane of the truncated cone serves as transmission window 18 transmitting light. As indicated by arrows in FIG. 1, a part of light emitted from LEDs 12 passes through transmission window 18 and serves as emitted light in the forward direction (upward direction). A part of light emitted from LEDs 12 is reflected by aluminum plate 16 and serves as emitted light in the lateral direction (horizontal direction) and in the backward direction (downward direction).
In this way, by controlling the traveling direction of light emitted from the LEDs using a light flux controlling member, it is possible to obtain emitted light in the lateral direction and in the backward direction as well as in the forward direction. Therefore, by using the light flux controlling member (reflection surface) described in PTL 1, it is possible to make the light distribution characteristics of the illuminating apparatus (LED lamp) close to the light distribution characteristics of an incandescent lamp to a certain extent.